A. Field of the Invention
The present invention relates to a protective film of a semiconductor device provided with an element active portion and an element peripheral portion.
B. Description of the Related Art
According to a technique as shown in FIG. 14, an inorganic insulating film such as a silicon oxide film or a silicon nitride film is formed as inorganic protective film 10 on gate metal wiring 31, channel stopper electrode 32, source electrode 33 and field plate electrodes 12 which are made of a metal material and which are formed on an upper surface of semiconductor substrate 100. Further, an organic insulating film such as a polybenzoxazole film or a polyimide film is formed as an organic protective film on an upper surface of inorganic protective film 10.
In order to stabilize characteristics of a semiconductor device and improve voltage withstanding thereof, a first insulating layer is formed to lie across an emitter electrode and a gate electrode and a second insulating layer is formed in upper and side surfaces of the first insulating layer. The gate electrode is partially covered with the first insulating layer (for example, see JP-A-2010-161240).
In JP-A-2008-227236, a guard ring electrode and a source electrode in a termination region of a semiconductor element are covered with a protective film made of silicon nitride or polyimide, or the like, in order to reduce the influence of external charges.
In JP-A-2011-204710, field plate electrodes in a termination region of a semiconductor element are covered with a separation oxide film or an interlayer insulating film in order to reduce the influence of external charges and increase the withstand voltage in an element peripheral portion.
In JP-A-2001-230505, a plurality of dielectric layers made of an inorganic material and an organic material are superimposed on one another as a passivation layer on a conductive layer so that the time for a dry etching step for opening the passivation layer is shortened and mechanical stress applied to a silicon nitride layer is relaxed.
In JP-A-8-293492, a polyimide film is formed as a passivation film on a silicon nitride film and ashing is performed on a surface of the polyimide film in order to prevent corrosion of a metal wiring portion exposed in an opening portion of the passivation film and improve the adhesion between polyimide and a mold resin.
The protective film according to the background-art technique shown in FIG. 14 has a double-layer structure in which the inorganic protective film is formed on the surface of semiconductor substrate 100 and the organic protective film is formed thereon. The protective film is formed in order to prevent entry of ions in a mold resin and moisture from the outside in addition to protection against foreign matters on the surface of an element peripheral portion Y of the semiconductor device or against a filler attack caused by a filler in the mold resin. This protective film plays a role of keeping an electric field distribution of the element peripheral portion Y and preventing withstand voltage deterioration.
However, there may be a case where cracks occur in the inorganic protective film in the element peripheral portion Y due to the stress applied to the semiconductor device in a fabricating step. When cracks occur in the inorganic protective film in the element peripheral portion Y, an electric field is locally concentrated in the place where the cracks have occurred in a reliability test in a high temperature and high humidity atmosphere such as a THB test (Temperature, Humidity, Bias Test) so that local decrease in the withstand voltage between a drain electrode and a source electrode occurs and leak failure occurs.
In addition, when the inorganic protective film which may cause occurrence of cracks is not formed, and only the organic protective film is formed, occurrence of cracks can be prevented. However, leak failure occurs between the gate electrode and the source electrode because moisture and ions in the mold resin enter into an interface between the protective film and the metal wiring and an interface between the protective film and a metal electrode in a reliability test in a high temperature and high humidity atmosphere such as a THB test. In addition, leak failure occurs between the gate electrode and the drain electrode when a ground voltage is applied to the source electrode and a negative voltage is applied to the drain voltage.